In EP 0 503 785 B1 processes for the preparation of olmesartan medoxomil is disclosed involving inter alia reacting (5-methyl-2-oxo-1,3-dioxolen-4-yl)methyl-4-(1-hydroxy-1-methylethyl)-2-propylimidazole-5-carboxylate and 4-[2-trityltetrazol-5-yl)phenyl]benzyl bromide in N,N-dimethyl acetamide in the presence of potassium carbonate, or reacting ethyl-4-(1-hydroxy-1-methylethyl)-2-propylimidazole-5-carboxylate and 4-[2-trityltetrazol-5-yl)phenyl]benzyl bromide in N,N-dimethylformamide in the presence of sodium hydride. In example 70 the alkylation of ethyl-4-/1-hydroxy-1-methylethyl)-2-propylimidazole-5-carboxylate with 4′-bromomethylbiphenyl-2-carbonitrile in N,N-dimethyl acetamide and in the presence of potassium t-butoxide is disclosed. Common to all the processes disclosed is that the alkylated product is subjected to a column chromatography in order to obtain an acceptable purity. For the preparation of an ester, the product obtained is described to be hydrolyzed by means of an alkali metal hydroxide, the salt is isolated and further esterified. In the last step, the trityl protection group is removed by reacting the trityl medoxomil ester in acetic acid.
In J. Med. Chem., 39 (1996), 323-338 the alkylation step between 4-[2-trityltetrazol-5-yl)-phenyl]benzyl bromide or its analogues and the imidazole intermediate is described to have been performed in N,N-dimethyl acetamide and in the presence of potassium t-butoxide. EtOAc and water is added to the reaction mixture and the product is extracted into EtOAc. The purification of the product is achieved by the use of flash column chromatography (EtOAc/hexane, 1:2) and optionally by an additional crystallization from IPE, hexane, EtOAc or mixtures thereof.
In EP 0 796 852 B1 the authors disclose a safer and easier preparation of 5-substituted tetrazoles without the use of Bu3SnN3. The process comprises reacting a nitrile with an inorganic azide salt in an aromatic hydrocarbon solvent in the presence of an amine salt.
In WO 2004/085428 there is described a new process for the preparation of olmesartan medoxomil. In the process the ring in 4,4-dimethyl-2-propyl-1-{4-[2-(triphenyl-methyl-tert-azole-5-yl)phenyl]phenyl}methyl-4,6-dihydrofuran[3,4d]imidazole-6-one is opened, and the resulting 4-(1-hydroxy-1-methylethyl)-2-propyl-1-{4-[2-(triphenyl-methyl-tert-azole-5yl)-phenyl]phenyl}methylimidazole-5-carboxylic acid is subsequently condensated with 4-bromo(or chloro)methyl-5-methyl-2-oxy-1,3-dioxyheterocyclopentene under the action of alkali. After deprotection of the triphenylmethyl protective group, olmesartan medoxomil is obtained.
WO 2004/083213 relates to compounds represented by the following formula (II) and their pharmaceutically acceptable salts, and to a process for their preparation. They are used as intermediates for the preparation of angiotensin II receptor antagonist, e.g. olmesartan medoxomil.

A general shortcomings of the prior art methods resides in that processes proposed involve, apart from applying column chromatography, additional isolation steps, which are acknowledged to decrease yield and rendering any process cumbersome. Also the use of some solvents, such as acetic acid, in late reaction steps require additional crystallization/purification steps, since especially acetic acid is known to potentially lead to the formation of persistent impurities during the drying process and is also difficult to remove from the pharmaceutically active compound when present as a residual solvent.
In view of the shortcoming of the prior art an object of the present invention resides in providing an alternative process for obtaining olmesartan medoxomil, which may be rapidly carried out, is economical and provides the desired compound in high purity.